Photoelectric conversion elements equipped with a laminate having an N-type semiconductor layer and a P-type semiconductor layer disposed between opposing electrodes have been conventionally developed. Such photoelectric conversion elements generate photocarriers by photoexcitation so that electrons and holes move through the N-type semiconductor and the P-type semiconductor, respectively, to create an electric field.
Most photoelectric conversion elements currently in practical use are inorganic solar cells which are produced using inorganic semiconductors made of silicon or the like. The inorganic solar cells, however, are utilized only in a limited range because their production is costly and upsizing thereof is difficult. Therefore, organic solar cells produced using organic semiconductors instead of inorganic semiconductors have received attention.
In organic solar cells, fullerene is used in most cases. Fullerene is known to function mainly as an N-type semiconductor. For example, Patent Literature 1 discloses a semiconductor heterojunction film formed using an organic compound serving as a P-type semiconductor, and fullerenes. Fullerene, however, is known to be responsible for degradation of organic solar cells produced using the fullerene (see e.g., Non-Patent Literature 1). Thus, there is a demand for a material that substitutes for fullerene.
In the organic solar cells, a laminate having an N-type semiconductor layer and a P-type semiconductor layer disposed between opposing electrodes is generally encapsulated using an encapsulation resin such as a sealing material (see e.g., Non-Patent Literature 2). However, the problem of the organic solar cells encapsulated using an encapsulation resin such as a sealing material is that, depending on the type of a semiconductor material, the semiconductor material is degraded during encapsulation, resulting in reduced photoelectric conversion efficiency (initial degradation).